title: Activation of NADPH oxidase 4 in the endoplasmic reticulum promotes cardiomyocyte autophagy and survival during energy stress through the protein kinase RNA-activated-like endoplasmic reticulum kinase/eukaryotic initiation factor 2α/activating transcription factor 4 pathway.
abstract: BACKGROUND
  Autophagy is an essential survival mechanism during energy stress in the heart. Oxidative stress is activated by energy stress, but its role in mediating autophagy is poorly understood. NADPH oxidase (Nox) 4 is an enzyme that generates reactive oxygen species (ROS) at intracellular membranes. Whether Nox4 acts as a sensor of energy stress to mediate activation of autophagy is unknown.
  
  
  OBJECTIVE
  We investigated whether Nox4 is involved in the regulation of autophagy and cell survival during energy stress in cardiomyocytes.
  
  
  RESULTS
  Production of ROS in cardiomyocytes was increased during glucose deprivation (GD) in a Nox4-dependent manner. Protein levels and the ROS-producing activity of Nox4 were increased in the endoplasmic reticulum (ER), but not in mitochondria, in response to GD. Selective knockdown of Nox4, but not Nox2, or selective reduction of ROS in the ER with ER-targeted catalase, but not mitochondria-targeted perioxiredoxin 3, abrogated GD-induced autophagy. Nox4 promoted autophagy during GD through activation of the protein kinase RNA-activated-like ER kinase pathway by suppression of prolyl hydroxylase 4. The decrease in cell survival during GD in the presence of Nox4 knockdown was rescued by reactivation of autophagy by Atg7 overexpression, indicating that the effect of Nox4 on cell survival is critically mediated through regulation of autophagy. Nox4 was activated during fasting and prolonged ischemia in the mouse heart, where Nox4 is also required for autophagy activation and cardioprotection.
  
  
  CONCLUSIONS
  Nox4 critically mediates autophagy in response to energy stress in cardiomyocytes by eliciting ROS in the ER and stimulating the protein kinase RNA-activated-like ER kinase signaling pathway.
authors.affiliation: From the Department of Cell Biology and Molecular Medicine, Cardiovascular Research Institute, Rutgers New Jersey Medical School, Newark (S.S., P.Z., D.S., D.Z., N.N., J.S.); IRCCS Neuromed, Pozzilli (IS), Italy (S.S., M.V.); Department of Internal Medicine, University of Texas Southwestern Medical Center at Dallas (L.S.T.); and Department of Clinical/Molecular Medicine, School of Medicine and Psychology, Sapienza University, Rome, Italy (M.V.).
authors.forename: Sebastiano
authors.initials: S
authors.lastname: Sciarretta
authors.forename: Peiyong
authors.initials: P
authors.lastname: Zhai
authors.forename: Dan
authors.initials: D
authors.lastname: Shao
authors.forename: Daniela
authors.initials: D
authors.lastname: Zablocki
authors.forename: Narayani
authors.initials: N
authors.lastname: Nagarajan
authors.forename: Lance S
authors.initials: LS
authors.lastname: Terada
authors.forename: Massimo
authors.initials: M
authors.lastname: Volpe
authors.forename: Junichi
authors.initials: J
authors.lastname: Sadoshima
mesh_terms: D051701:Activating Transcription Factor 4 / Q000502:physiology*; D000818:Animals; D001343:Autophagy / Q000502:physiology*; D002470:Cell Survival / Q000502:physiology; D004721:Endoplasmic Reticulum / Q000502:physiology*; D004734:Energy Metabolism / Q000502:physiology; D015852:Eukaryotic Initiation Factor-2 / Q000502:physiology*; D066298:In Vitro Techniques; D051379:Mice; D018345:Mice, Knockout; D023421:Models, Animal; D032383:Myocytes, Cardiac / Q000166:cytology / Q000502:physiology*; D000074663:NADPH Oxidase 4; D019255:NADPH Oxidases / Q000172:deficiency / Q000235:genetics / Q000502:physiology*; D018384:Oxidative Stress / Q000502:physiology; D017382:Reactive Oxygen Species / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology; D013312:Stress, Physiological / Q000502:physiology*; D015854:Up-Regulation / Q000502:physiology; D019892:eIF-2 Kinase / Q000502:physiology*
chemical_list: D051701:Activating Transcription Factor 4; D015852:Eukaryotic Initiation Factor-2; D000074663:NADPH Oxidase 4; D019255:NADPH Oxidases; D017382:Reactive Oxygen Species; D019892:eIF-2 Kinase; C081452:Atf4 protein, mouse; C422943:Nox4 protein, mouse
keywords: NOX4 protein; autophagy; endoplasmic reticulum; fasting; myocardial ischemia; reactive oxygen species